FRIDAY, April 27 (HealthDay News) -- People undergoing outpatient surgery should be warned about their risk for dangerous blood clots, according to a new study that finds the risk is higher among groups including, but not limited to, those who are older or obese.

The University of Michigan researchers found that one in 84 patients considered high-risk suffers a blood clot after outpatient surgery. More than 60 percent of operations are currently performed as outpatient procedures, according to background information in a university new release.

"Outpatient surgery now includes a greater variety of procedures, from
plastic surgery to cancer operations and orthopedic surgery, and not all patients are young, healthy individuals," lead study author Dr. Christopher Pannucci, a University of Michigan plastic surgeon, said in the news release. "These data are in stark contrast to provider and patient expectations that outpatient surgery is a low-risk event."

The researchers looked at more than 200,000 outpatient surgeries across the United States, and found that most patients had more than one risk factor for developing a clot, known as a venous thromboembolism. These clots form in the veins (deep vein thrombosis or DVT) and can be deadly if they travel to the lungs (pulmonary embolism).

The study, published online April 13 in Annals of Surgery, concluded that improved patient screening is needed to prevent these dangerous blood clots. Factors to consider include:

The researchers, who have created a tool that clinicians can use to measure a patient's risk for blood clot following outpatient surgery, said their findings could help improve how patients are informed about their surgical risks.